1. Field of the Invention
The present invention relates to such a ship's propulsion and/or steering unit arrangement, at least partly surrounded by water, that comprises an electric motor in a substantially sealed chamber formed by the unit walls, a propeller shaft associated with said electric motor having a propeller or a similar device fitted outside said chamber for transmitting the electric motor's power as motion energy into the surrounding water. The present invention further relates to a method for managing fluid flows in the propulsion and/or steering unit presented above. The present invention also relates to an arrangement for improving the efficiency of the cooling of a propulsion device's motor in a propulsion and/or steering unit as discussed above.
2. Discussion of Related Art
Previously known are propulsion units for ships or similar devices operating on a water surface, said devices comprising outside the actual hull a substantially sealed chamber within which an in most cases electrical motor is arranged. The motor shaft functions either directly or by means of a suitable gearing as a propeller shaft, which outside the chamber has a propeller fitted for transforming the motor power into a flow of water driving the ship. In most modern arrangements, this kind of chamber is, in addition, fitted rotatably about the vertical axis, in which case the device at the same time functions both as a ship's propulsion and steering means. The applicant provides devices of this kind with the trade mark Azipod™.
Such so-called pods are disposed underneath the water surface, at least as concerns their substantial part, and usually there is arranged a connection to the inside of the hull through a vertical shaft tube or similar. At least when the ship is in water, the entrance e.g. for maintenance takes place via this connection, which often is rather cumbersome. Since, however, an underwater shaft arrangement is associated with the arrangement, in which arrangement one part of the shaft is inside the chamber and the other part outside, there always is a certain possibility of leakage, in which case this kind of leakage must be detected and any possible raising of the water level in the chamber must be stopped. Since the chamber often is disposed in a substantially cold water, there is at the same time a risk that e.g. humidity in the cooling air is condensed at the chamber walls, which also results in water accumulating on the bottom of the chamber. Due to these reasons, the arrangement has this far required specific control and pumping arrangements to be arranged in the chamber.
In the same way, also during operation there is a need to perform in the chamber different maintenance measures associated with the functioning of the motor and the rest of the equipment, the purpose of which is on the one hand an ensuring of sealing and on the other hand a continuous maintaining of different lubrication and similar functions.
Further, motor arrangements having a structure of the aforementioned type have been developed, in which the heat generated by the electric motor is, at least for its substantial parts, conducted directly into the surrounding water. In such a structure, the motor body functions as an intermediate means for transmission of heat, in which case the surface of the pod, in turn, functions as a cooler. In that case, one of the problems has involved poor transmission of heat from the stator into the motor body and from it further into the pod housing.